Fluorescence microscopes of this type are widely used in fluorescence studies in which a fluorescent sample or specimen is studied. If required, a sample which does not fluoresce per se can be provided with a fluorescent substance. If such a sample or specimen is irradiated with suitable light, usually but not exclusively visible light or ultraviolet light, the fluorescent substance in the sample will light up with fluorescent light which has a longer wavelength than the excitation light. Frequently, the intensity of the fluorescence is low, which means that in virtually all cases the excitation light is filtered out with the aid of a filter. The weak fluorescence is then, in principle, the only visible image.
In practice, fluorescence studies are often carried out on microorganisms. This usually involves higher magnification, preferably more than 50 times up to 100 times at the objective, and around 1000× in total to enable inspection by means of the human eye. On top of this, a typical size of a substrate used is, for example, a diameter of 25 mm. Such a size is often necessary, for example, in the case of micro-biological samples, where a certain amount of sample fluid should pass through the substrate in order to get the microbiological particles which are to be studied subsequently, concentrated on the substrate. In the process, the sample fluid passes through thin perforations in the substrate, and the particles remain behind on the surface of the substrate.
A drawback of the known fluorescence microscope is that the measuring time can become very long. In the case, for example, of microbiological studies at a desired resolving power less than 1 micrometer and a substrate having a diameter of 25 mm, with a measuring time of a few seconds per image, a total measuring time of many hours up to a day, even, is not exceptional.